As has been said, the battery provides the energy which causes the electrons
to move and results in the electrical current. Energy is measured in Joules
and it can be said that energy stored in the battery is transferred to the circuit
as the battery is used.

Household appliances, such as electric light bulbs, are marked in Watts. Bulbs
can be 40 Watts, 60 Watts 100 Watts etc. The Wattage is a measure of power.

Power is the rate at which energy is transferred
from electrical to other forms, such as light and heat in a bulb.

A 40 Watt bulbtransfers energy to light and heat at a rate of 40
Joules per second.

A 60 Watt bulb transfers energy to light and heat at a rate of
60 Joules per second. etc.

A household is charged according to the electricity that it uses. This depends
on both the power of the appliance used and the length of time for which it
is on. A 100 W bulb obviously transfers electrical energy to heat and light
more quickly than a 40W bulb and so is more expensive if it left on for the
same length of time. A kettle usually has a power rating of 3 kiloWatts which
means 3000 Watts but it is usually only on for a short period of time.

It makes sound economical and ecological sense to invest in low energy light
bulbs, which have a Wattage of about 8 to 20 Watts. This is particularly true
where bulbs are likely to be left on for a considerable period of time.